Waitrose chicken

Yesterday I bought some diced chicken at Waitrose. Was about to cook it today and noticed it was smelly. I don't have the receipt anymore. I do have the chicken and the packaging. Do you think they'll take it back and refund it without a receipt? It has a use by date of 21st April.

Update - returned the even smellier chicken to Waitrose this morning. They offered to exchange it for another pack, which I declined, and they refunded me twice what it cost to buy initially.No problems about having no receipt. Result.